氢键铁电有机小分子体系中质子转移过程的实空间研究

Hydrogen bonded ferroelectrics based on small organic molecules has attracted great attention due to its potential application in ultra-dense information storage and in low-field and above-room-temperature operation. Proton transfer induced by electric field is a key factor in the determination of the ferroelectric properties of the materials. In this project, we plan to focus on the real-space research of proton transfer process in model systems of hydrogen bonded ferroelectric molecules, by using scanning tunneling microscopy (STM) and qPlus atomic force microscopy (qPlus AFM). Electric field under STM tip will be used to break the covalent bond in the hydrogen bond and to release a proton, in order to simulate the proton transfer process in hydrogen bonded ferroelectrics. Atomic resolved molecular configuration and charge distribution during this process will be studied by using qPlus AFM. In addition, the side groups connected to the molecular backbone will be adjusted, in order to manipulate the hydrogen bond interaction between molecules. The influence of the connected side groups together with the thickness of the molecular films on the proton transfer will be systematically studied. We expect that the results obtained from this project can provide direct experimental information for the deeper understanding of the ferroelectric mechanism in small molecule systems. Furthermore, to build the relationship between proton transfer process and molecular structure/film thickness, might be a guide for the design and development of new organic ferroelectric systems.

氢键铁电有机小分子体系因其在超高密度存储方面的潜在应用及低电场室温条件下的可操控性而备受关注。电场作用下的质子转移过程是决定这一类材料铁电性质的关键因素。在本项目中，我们将利用高分辨的扫描隧道显微镜（STM）及qPlus原子力显微镜（qPlus AFM）技术对氢键铁电有机小分子模型体系中的质子转移过程进行研究。申请人拟利用STM针尖电场诱导氢键中连接氢原子的共价键断裂来实现质子的自由移动，以此模拟氢键铁电的质子转移过程，并利用qPlus AFM技术对该过程中分子的微观构型及电荷分布进行研究。另一方面，申请人将改变与分子骨架相连的基团来调控分子间的氢键相互作用，并研究该因素以及分子膜的厚度对质子转移过程的影响。通过此项研究申请人希望可以为理解有机小分子体系的铁电性质提供直接的实验数据，并建立质子转移过程与分子结构、薄膜厚度的关系，为设计和研发性能优越的有机铁电分子体系提供依据。

作为一类性能优越的单组分氢键铁电体系，铁电性质可调控的苯并咪唑基分子成为本项目研究的模型体系。器件尺寸的不断小型化为功能分子薄膜制备技术的发展提供了契机，探索高质量薄膜的生长条件成为研究热点。薄膜的性能与结构紧密相关，因此有必要对薄膜中分子的结构及分子排列方式进行深入研究。本项目利用扫描隧道显微镜技术对比研究了携带不同官能团的两种苯并咪唑基分子在Au(111)衬底表面的薄膜生长条件以及薄膜中分子的排列方式，并对分子间氢键、分子与衬底间相互作用以及分子结构热稳定性进行研究。研究结果表明连接羟基苯基的苯并咪唑基分子相比连接羟甲基的苯并咪唑基分子，其与衬底间的相互作用更弱，分子更容易规则排列形成高质量薄膜。本研究为选择适当功能分子进行薄膜制备提供了一定的依据。